Test tubes (or culture tubes) are common chemical vessels consisting of a length of glass (or sometimes plastic) tube open at the top and sealed at the bottom. They come in a variety of diameters and lengths and may have a flared rim or be rimless (straight).
Test tubes may be used as reaction vessels, short-term storage containers (when stoppered), or for heating small amounts of substances. An inverted test tube filled with water may be used to trap gases produced during a chemical reaction.
Test tubes used in the chemistry lab are usually made from thermally stable borosilicate glass so they can withstand high temperatures and corrosive chemicals.
During heating, test tubes are typically held with a clamp or tongs placed approximately 1cm below the mouth of the test tube. The tube is tilted at an angle with the mouth pointing away from all people in the lab. Tilting the tube allows the bottom to be heated to very high temperatures while the top of the tube remains fairly cool.